The investigators seek to elucidate the roles of specific air pollutants, and inter-relationships among them, in producing acute exacerbations of certain cardiac and respiratory conditions, using two complementary approaches. First, the study period of an ongoing study of emergency department (ED) visits in Atlanta will be doubled and multi-pollutant questions will be addressed in the resulting unique and powerful database. This study is an investigation of cardiac and respiratory ED visits in relation to daily measures of air quality, including detailed measurements of particulate matter (PM) components being conducted at the station operated for the Aerosol Research and Inhalation Epidemiology Study (ARIES) in downtown Atlanta. The existing study period is August 1998 through August 2000. Operation of the ARIES station is being extended through August 2002, and in this application the investigators are seeking to extend ED outcome data collection for this period. With data on over a million ED visits per year, this study may be the largest single-city ED study with speciated PM data to date. As such, the expanded study will be uniquely positioned to disentangle effects of PM from the effects of other pollutants and to contribute to our understanding of the effects of exposure to PM in the presence of other pollutants. Moreover, the detailed air quality data available to the investigators will allow assessment of the role of PM components (e.g., sulfates, water-soluble metals) and size fractions in the multi-pollutant analysis. Second, a companion study of unscheduled admissions to Atlanta-area hospitals by elderly Medicare beneficiaries, is planned. Given that the investigators will have already compiled a comprehensive air quality database and will have established the time-series modeling methodology, this second substudy will provide an efficient approach to assessing coherence in the results for similar conditions across clinical care venues as well as direct comparability to the numerous other studies that have employed Medicare data. Finally, a thorough assessment of the role of measurement error in the epidemiologic analyses will be performed.